Why look at different frequencies of light? Cooler objects are only visible at long wavelengths: radio, microwaves, IR. Hotter objects are only visible at short wavelengths: UV, X-rays,  -rays.

Radio Telescopes Detects cool gases: H + H H 2 Can detect molecules out in space: oxygen O 2 carbon dioxide CO 2 hydrogen cyanide HCN formaldehyde H 2 CO Ethanol CH 3 COOH

Advantages / Problems Operates night or day Atmosphere doesn’t absorb radio waves Poorest resolution of any type of light (doesn’t see details well) Solution is to make antennas (dishes) VERY large

Arecibo Radio Telescope, Arecibo, Puerto Rico

Puerto Rico

Green Bank Telescope Green Bank, W.Va. The dish would hold Fulton Field

Radio Interferometry – a Recipe Take 2 (or more) widely separated radio telescopes… Electronically blend their signals… Result is as if you had a telescope with a diameter equal to the distance between the two separate telescopes. VASTLY improves resolution!

Very Large Baseline Array sites across the US. Together these telescopes form a huge interferometer.

Infrared (IR) Telescopes Very similar to visible wavelength telescopes, except for the detector, called a bolometer. IR scopes detect heat from warm gas or warm objects. “Warm” means not hot enough to glow in visible light. These scopes must be kept very cold or the heat the scope itself radiates swamps out what they’re looking for.

What kinds of objects? IR telescopes “see” warm gas, molecules & dust. In some cases, they can look through cooler dust to see what’s inside the dust clouds! Since stars form where there’s lots of dust, these scopes are great for looking inside dusty nebulas where new stars form.

We can’t see everything just in visible wavelengths !!

ISO – the Infrared Space Observatory European Space Agency (ESA)

Orbital Telescopes Why put a telescope in orbit? Gets it above the atmosphere with all its dust, ozone, water vapor, and CO 2 that absorb so much of what we want to see. What’s the most famous orbiting telescope? If you said the Hubble Space Telescope or HST, you’re right!

HST does detect visible light It also detects ultraviolet light. 2.4 meter mirror = 230,400 eyes! Resolution is arcsecond or 1 / 3,500,000 th of a circle. We’re used to seeing photos like these!

X-ray & Gamma Telescopes “Sees” very hot objects: Black Holes Pulsars & Neutron Stars Supernovas VERY good resolution – sees fine details

NGC 4261 – a huge black hole at the center of a distant galaxy

A supernova – an exploding star

What’s left after the explosion – a supernova remnant. This one’s called Cassiopeia A.

The Crab Nebula in visible light (left) & X-rays (right).

At the center of the Crab Nebula – a PULSAR